Both vitamin D.sub.2 and vitamin D.sub.3, their hydroxylated metabolites, as well as some of their structural analogs are known as effective regulators of calcium and phosphate homeostasis in the animal or human. These compounds, therefore, have utility as therapeutic agents for the prevention and treatment of disorders of calcium and phosphate metabolism, such as rickets, osteodystrophy, osteomalacia, osteoporosis and related mineral imbalance conditions.
Known compounds of this class are characterized generally by a saturated steroid side chain (as in the vitamin D.sub.3 series) or a 22-trans-unsaturated side chain with a 24-methyl substituent (as in the vitamin D.sub.2 series). The compounds of the present invention are side chain-unsaturated, but are distinguished by the presence of a 23-trans-double bond from the known vitamin D.sub.2 metabolites which include 25-hydroxyvitamin D.sub.2 (U.S. Pat. No. 3,585,221), 1.alpha.,25-dihydroxyvitamin D.sub.2 (U.S. Pat. No. 3,880,894) as well as the 24-hydroxy- and 24,25-dihydroxyvitamin D.sub.2 compounds (Jones et al. Arch. Biochem. Biophys. 202, 450 (1980)).
Other vitamin D.sub.2 structural analogs that have been prepared include 1.alpha.-hydroxyvitamin D.sub.2 (U.S. Pat. No. 3,907,843), and certain side chain unsaturated compounds (Bogoslovskii et al. J. Gen. Chem. USSR 48(4), 828 (1978); U.S. Pat. No. 3,786,061) which, by virtue of containing 22,23-trans-double bond, may be considered 24-desmethyl derivatives of vitamin D.sub.2. Another compound structurally related to the products of the present invention is 23-dehydro-25-hydroxyvitamin D.sub.3 (U.S. Pat. No. 4,360,471).